Automatic clutch



Dec. 22, 1953 w.:r. LIVERMORE AUTOMATIC CLUTCH lFiled Jan. 29, 1949 INVENTOR.

WML/AM 7.' L/vA-'RMORE y? Patented Dec. 22, 1953 UNITED STATES ATENT orrlclzA v 27 Claims. l

This invention relates to automatic transmissions for self-propelled vehicles and more particularly to improvements in the control system for effecting automatic engagement of a friction clutch employed in engaging drive.

In my United States Letters Patent Nos. 2,638,- 035 and 2,604,197, I have disclosed progressive developments in an automatic transmission em ploying a pair of friction clutches which are alternately engaged to produce drive from the engine to the propellershaft through a plurality of gear trains of diiferent ratios and the present application forms a continuation in part thereof. In each of such prior applications one or more complete transmission units is shown including the automatic control system'for effecting shifts from one speed ratio to another as well as fer initiating drive through the engagement of a low speed clutch. The low speed clutch engagement in each case has been eiected through the combined or differential operation of a mechanism responsive to engine speed, together with a iiuid pressure actuated mechanism responsive to accelerator position. Such devices have operated to urge clutch facings together with a force limited by the effective accelerator controlled duid pressure as well as by the effective engine speed, the conventional manually operated clutch pedal being completely dispensed with.

In providing controls for automatic clutch engagement in a transmission f the type disclosed in my aforementioned prior applications a number of factors must be taken into consideration. It is desirable to provide low speed clutch engagement pressure eiective to establish initial drive in a manner relating such pressure to engine speed in order to accomplish smooth engagement of engine torque, avoid excessive slipping and, at the same time, obtain clutch pressure which will vary with the degree of acceleration required. On the whole, a uid pressure actuated clutch engagement centrifugally controlled to provide clutch pressure increasing with engine speed is saisfactory under normal driving conditions.

One problem in automatic clutch engagements arises in cars which are equipped with devices for producing high idling speeds during the warmn up period of the engine. It is clear that a centrifugally actuated clutch adjusted to produce initial clutch engagement at an engine speed slightly above normal idling speed would result in undesired clutch engagement when the engine is idling at an abnormally high speed with the vehicle at a standstill, unless some provision is made to avoid clutch engagement under such conditions. This latter problem was met lby a dnferential arrangement in my prior constructions whereby centrifugal effect responsive to en gine speed would normally control initial clutch engagement pressure subject to the limitation of the effective uid pressure controlled by the accelerator position. Thus, When the accelerator was released, a high idling speed was not effective to produce clutch engagement.

Clutch pressure control increasing with engine speed was obtained in the structures shown in the aforementioned Patent No. 2,633,635, and the first modiiication of Patent No. 2,604,197, through the use of a pluralityV of lever arms rotated at engine speed which were adapted to transform centrifugal force into clutch pressure. In such cases fluid pressure diaphragms or pistons formed reaction members for the weighted levers in a manner whereby clutch engagement could be ob tained only when sufficient fluid pressure, as controlled by accelerator position, was admitted to the diaphragme or pistons. This arrangement was satisfactory in operation, but comparatively expensive to manufacture.

In the second modiication of the latter applie cation, a centrfugally actuated valve was used in place of the weighted levers to produce clutch actuating l'iuid pressure increasing with 'engine speed. Such valve was arranged to block an exhaust port communicating witha clutch actuating diaphragm in a manner whereby the clutch actuating uid pressure required to open the valve would increase with the engine speed. Accelerator control was in this case obtained by a second valve blocking a second exhaust port with a force responsive to accelerator positionlThis construction was less expensive than the above mentioned lever arrangement, but still required a valve mounted in the rotating clutch assembly and'ol passages to and from the pump located in the stationary housing.

The principal object of the presentA invention is to provide an automatic clutch pressure con;

plate orifice in which the length of the orifice is small compared to its diameter, in order to minimize discharge variations arising from temperature changes in the oil.

Another object is to provide a control device of this type which will incorporate means for establishing a predetermined minimum fluid pressure preload in the clutch actuating mechanism independent of engine speed or accelerator position, such predetermined minimum being less than thel pressure required for initial `clutch en.- gagement so as to minimize any lag in clutch actuation incidental to building up initial pressure to overcome release springs and moving clutch facings to engaging position, and to keepthe' dia'- phragm full of oil.

A further object is to incorporate clutch pressure release means responsive-'to released:-accel-I erator position for preventing any initial clutch engagement when the accelerator is released even though the engine is idling at an abnormally high speed:

Another object-is to providea mechanism for blocking Athe-exhaust 'orifices in "order to obtain a rapid-build-up -of'clutch kpressure'to 'a predetermiriedMV value increasing with throttle open'- ing 'and `bnlysli'ghtly lessA than 'that required Vto prevent the clutchrrom lslipping.

A further object isito incorporate a 'simple adjustment whereby the relation between `lclutch pressure and' engine' speedmay 'be readily `adn justedr- Another object is to/use a single' engineY driven pump-"as va source of"'`u`id 'pressure-"for-'actuating both 'clutch and other controls.

A 'furtherobject is toA providemeans forbliocking-the discharge orifices'in" order that clutch release may 'be `avoided while' the' 'vehicle' is 'op'- eratingy in certain high speedgears'i'regardless of engine speed.'`

These and other objects 'will appear more clearly from the following detailed description of a particular embodiment of my invention and from"'anifexainination of the drawing wherein a schematic representation of fan orice type clutch pressurecdntrolmechanism is'shown.

With reference to the drawing, it`will beseen chata clutch ,diaphragm or piston I0, such as disclosed inrm'y aforementioned applications,

forms' a fluid pressure operated mechanism for producing 'a clutch engagement .pressure proportionalto the fluid pressure produced therein. An 'engine 'driven Ypump II.r draws fluid from the sump v'I'2"`and discharges the same into the deliverypassages I3,"'I'4"." Pressure builds'up in thesepassages' and inthe passage. I5 leading to huid pressure controlsio'r other' parts of the transmission "until jaA`predetermine'd maximum pressure', foriexample eighty 'poundsV 'per square inch,L is `established 'whereupon 'thepreload valve I6 opens-permitting' fluid under pressure Iso pass into conduits 'I1,"I8',the clutch actuating dia- 'phragm' 'I0 "and the orifice valve chamber I9. A 'return *passage 20V from the oriflce valve 4forms 'the'"only`'exhaust"for fluid vdelivered 7from 'the pump "with'the exception of that consumed 1intermittently 'by 'the 'other transmission controls, 'as vinshifting gears, separately `"eihzuisted to the sump and vwiththe exception of that vexhaustedv bythe pressure control valve, as hereiliafte'r described. y

AS shWn in thedrawing, the main orifices 20a are blocked'by a valve piston 2I which Ais heldv in acting against the small end 24 of a reduced seetion of the valve piston 2|. A relay valve 25. within the bore of which the valve piston 2I operates, is held by a spring 26 against a valve seat 21 so that the only open passage from the valve chamber I9 to the exhaust chamber 20 is through the adjustable orifice 28 employed to compensate for commercial variations in pump discharge. Fluid pressure in the chamber 23 is vcontrolled by the pressure controlivalve 29 which is in turn responsive tothe position of the accelerator 30, as will be hereinafter more fully described.

The operation of the orifice and relay valves may be seen by following through' a typical example. Assuming that an engine is started and warmed up to normal operating temperature and idlingvspeedythe-engine driven pump II will deliver. fluid to passages I3, I4, I5 as well as to the pressure control valve 29. Assuming that the accelerator is in a released position, no pressure will be exerted on 'spring 3I and no positive pressure will exist in the conduit 32 or chamber 23 since any such pressure would communicate through passage 33v to the end of the' small plunger 34 moving the control valve 29 to an exhaust position. When the pressure in passages I3, I4 and I5 has reached the predetermined required operating vpressure for the other transmission controls, the preload valve I6 will open and full delivery of the pump, with the exception of a small amount passing through the adjustable orifice 23, will be available'to produce pressure against the clutch diaphragm I0 until a predetermined pressure less than that required to overcome the clutch release springs is established in the Valve chamber i9. At this time the relay valve 25 will be moved against the pressure of spring 26 permitting discharge'through seat 21 and passage 2! to the sump. Since spring 22 is strong enough to resist a greater pressure in chamber I, plunger y2| will be held to the left, keeping oriiices 26a closed.

Assuming that the accelerator is now depressed to a position for slow acceleration, a light pressure Will be exerted on spring 3|' permitting the establishment of a light pressure in passage 32 and chamber 23 to Vbring about a'balanced condition of the pressure control valve. Such pressure in the chamber 23 will operate against the large area of the relay valve 25 to move it against its seat and will also act on the small end 2li of the piston 2I assisting spring 22 to urge such piston to the-left and keep the orifices 28a closed. As long as oriiices'a remalnclosed, the pressure in chamber I2 and clutch diaphragm I0 is proportional to the firmness with which lthe relay valve is pressed against yseat 21 'by its spring 26 and the pressure in chamber2'3.

If 'the acceleratoris now depressed a little more, slightly greater pressure will be exerted on spring V3l, permitting the establishment of slightly greater pressure'in 'passage '32 'and chamber '23. The clutch pressure 4'can 'jthus beV icontrolled entirely in "accordance with accelerator positionup'to a value such lthatits force on'the larger end of plunger 2|' becomes great enough to overcome spring 22 plus the pressure "of the fluid in chamber 23I upon the smaller end 24 of plunger 2I causing 'orifices 2da to open. if the engine speed is again slightly increa'sedby opening the throttle still further, :the clutch actuating pressure will be controlled by the 'flow'rv of oil through orifices 2111iA and will'increase substantially in proportion tothe squareof such engine speed until'sufcient pressure is established to overcome clutch slippage. It can, of course, never be greater than a maximum pressure determined by the maximum value of the fluid pressure transmitted to chamber 23 by the pressure control valve, which is in turn limited by safety Valve I5.

If the accelerator had been depressed to a still more Wide open throttle position, a heavier pressure in the chamber 23 Would cause the piston 2| to hold the main orifices 29a closed until a still higher predetermined pressure had been established in the clutch actuating diaphragm l after which the main orices 20a would take 'over control of the clutch pressure.

It will be seen that with this arrangement the clutch is preloaded during normal idling speed to partially overcome the clutch release springs so that a slight additional pressure incident to an initial increase in pressure in chamber 23 upon depression of the accelerator will be suflicient to produce prompt initial clutch engagement. Since-the discharge of the engine driven pump can flow only to the actuating diaphragm lil, the only lag incident to the production of initial clutch engagement is that caused by the necessity of expanding the diaphragm in order to move the clutch facings together.

The limit up to which the clutch pressure is entirely controlled by the accelerator can be high or low according to the Weight of spring 22, and the areas of the large and small ends of plunger 2 l. It should not be more than the light pressures used for maneuvering the car With the clutch slipping. It can be made less than the clutch release spring pressure if spring 22 is made very light. The final clutch pressure would then be entirely controlled by the orifices in accordance with engine speed for any throttle opening.

The case will now be considered Where the engine is cold when started and is provided with a high idling device which would cause the engine to run when idling above the speed at Which initial clutch engagement would normally take place. Since the accelerator is in released position, no fluid pressure will be exerted in chamber 23 against the ends of the relay valve 25, andthe spring 2E is of such a Weightas to cause the relay valve to be opened by clutch actuating pressure just prior to the establishment vof clutch engagement thereby preventing clutch engagement as long as the accelerator remains released. Upon depression of the accelerator 36, pressure in the chamber 23 urges the relay valve 25 toward its seated position thereby causing clutch actuating pressure to buildup in accordance With accelerator position The clutch is thus controlledl by the accelerator until it is depressed sufficiently to cause the engine lto slow down to a point Where the delivery of the engine driven pump is passed by the orices' and 2lla'after which the clutch pressure will be controlled by such orifices in normal operation. In certain speed ratios it is undesirable to have vthe clutch release 'at low engine speeds, particularly when ascending a hill or acceleratingwith open throttle.

A lookup plunger 35 may therefore be actuated when the vehicle is traveling in such higher speed ratios to hold the piston 2l in its closed position in order to maintain clutch engagement pressure limited only by the pressure of spring 26 and the iiud pressure in. chamber 23, holding relay valve 25 ,against its lseat 21. LThis device could also be used te obtain engine braking action' in *such higher speed ratios regardless 'of the speed of the engine. Satisfactory means for actuating the Vlock-up plunger 35 are shown in my prior Patent yit is unnecessary to incorporate the clutch pressure control mechanism in rotating portions of the clutch assembly, thereby reducing substantially the cost of manufacture. In addition, the arrangement shown permits a rapid build-up to predetermined clutch engaging' pressures determined by accelerator position, together with engine speed responsive control for clutch pressures above such predetermined engaging pressure.

It will be noted that while the centrifugal valve disclosed in my prior Patent No. 2,604,197 could lbe spring loaded to give a predetermined minimum pressure short of that required to produce initial clutch engagement when the engine was running, no means were provided for the delayed opening of such valve pending the establishment yof minimum actuating pressures varying with and controlled by accelerator position. Thus, AWhereas my prior accelerator control Was inherently conned to limiting the clutch pressure to some value less than that corresponding to engine speed, the present accelerator control may be employed Where desired to control clutch pressures inexcess of those corresponding to engine speed, either, for. example, to produce partial clutch engagement during parking maneuvers or to control establishments of predetermined portions of pressures required to overcome slippage for various throttle openings. Such latter feature is another contributing factor to the elimination of lag in response and'is believed to be partially responsible for the highly successful operation of the orifice controlled system.

1. A drive engagement control adapted for use in a self-propelled vehicle having ran engine, a manually operated throttle'linkagefor controlling the speed of said en gine, adrivenshaft, and gradually engageable coupling means for establishingv drive betweensaid engine and shaft, comprising a iiuid pressure operated mechanism foreiecting coupling engagement, asource or" iiuid `pressure havinga volume "capacity increasing with` engine speed communicating with said mechanism, an: exhaust orice also communicating with said mechanism and proportioned relative to saidvolume' capacity in a Amannerfadapted vto eifect desired coupling engagement increasing with enginespeed a further exhaust passage, a'valve for blocking said latter exhaust passage urgedtoward an open position bysaid fluid pressure for effecting couplingengagement, and a source of iiuid pressure controlled by said throttle linkage' urging said valve to a closed pos'ition;v -f

2. A drive engagement `control adapted foruse in a selfipropelled vehicle having an engine, a driven 'shaft-'am gradually 'engageable coupling means .forestablishingfgdriva therebetween. coinprising a uuid pressure. opsratedmechanism for eieeting. coupling engagement-a source ot-iiuid pressure communicating .arithf said .mechanism having a. volume. Capacity vincreasins .with eneine speed, a coupling engagement pressure reemating exhaust crincealso communicating with Said, mechanism tor-controlling .the eiective coupling, actua-tine pressure. ari-orifice. blocking valve associatedtwith said. ex-haustoriee urged ley-such actuating pressure to angehen poSiticn,.-and means for holding said valve in its orificoblockingpositicn at pressures below `a predetermined minimum.

3. A .drive engagement.- control-system -asv set forth in :claim 2, including a manuallyoperated throttle linkage for controlling the spoed of said engine, a .source ofpr-.essure vvarying.,vyith ysaid throttle iinkage., and-means applying said latter pressure to said orice .blocking-- valve, whereby the coupling actuatingfpressure aft-Which said valve .will open saidf.critico-increases' with the progressively actuated position of--saiid .throttle linkage.

4. A. clutch control-.adapted for. usewinv a self.- propelled vehicle-.having fengine, a -rnanually operated throttle.linkageioncontrollings the speed of v.-said- .enginel a .driven shaft, -.and--a friction clutch for establishing, drive betvzeensaidengine and shaft. havingyieldable. clutch .release-means urging-.the clutch mem-bers out Iof. engagement, comprising a iiuid pressure operated mechanism for effecting clutch engagement, a source offfiuid pressure communicating; with 'said mechanism having a volume capacitv-increasinsvfith engine speedi .an exhaust orifice-.also viconnnunicating with said .mechanisrnj:forv controllingy theeiecltive clutch actuating. pressure, a valve .responsive `to such actuating pressure adopted to block the flow of. iiuid through .said orifice at.- pressures. .below Aa Predeterminedmfmimumfa iur-ther -exhaust pas:- sage, and a valve responsive. te thef operation fof said-...throttle linkage :fora-blocking said .latter passage.-

`5.` -A clutch .-pressurexcontrol system as set forth in claim e, wherein. the clutch actuating `pres.- sure atwhiehsaid,- nrstementionedivalvewill open said-.restricted passageis-made responsive tok .the position of.. said: throttle linkage-fin a manner whereby .increasingthrottlefopeningzwill result in higher clutch actuating pressures before said restricted passage. .becomes .operative in controlling clutch'pressure.:

ofAclutch control. adapted. for .use in a self propelled vehicle"having.-an-engine, .a .manual-ly operated throttle linkageV forcontrollingthc .speed of .said 'originen driven.. shaft,"` anda friction clutch :for establishingdrive between saideng-ine and shaft, .comprising a luidpressure operated mechanism for .effecting .clutch engagement, a source of fluid pressure. having a volume capacity increasing. with. .enginespeed communicatingv with said mechanism,..an.-.exhaustorice .also come municating with said mechanism. for ycontrolling the eiective clutch .actuating pressure, Va further exhaust passage, .a valve adapted .to blocksaid latter .passage and urged .to an opening position by .clutch actuatingeuid pressure, mechanism responsiveV tothe v.operation .of ...said throttle linkage'. for .establishing sa .source yof pressure, said latter. .source -of pressure .communicating with said valve in a, manner urging the same ,-to-a blockingposition-...-

7. 1Av clutch pressurecontrol system, as set. forth inclaini 2,.:1ncluding-.also .a -manualiy.;cperated throttle linkage for controlling` the speed of. said engine, -mechanism responsive -to the Aopeiuttion or said-throttle linkage for-.establishing .a source ofpressure varying with .the extent. ofthrottie openingsaid latter source of pressure .communicating with-said first-.mentioned valve in Va manner urging the same to a blocking position.

8,. Adrive engagement control adapted for-use inta selfspropelled. vehicle having an engrlero manually. operated throttle linkage for control.- lingthe-speed of said eneinei a .driven shaft. and gradually engageable coupling means. for establishing drivebetween said engine and shaft .haw ing-yieldable coupling release means urging the coupling members. out of engagement, vcomprising a fluid pressure operated mechanism for effecting coupling engagement, a source of fluid pressure communicating with said mechanism having a volume capacity. increasing with .engine speed, an exhaust orifice also communicating-with said mechanism for controlling the effective. coupling, .actuating pressure, mechanism responsive tothe operation of said throttle-linkage for establishing a Lsource ofpressure varying with the extent or vthrottle opening, a diierential. valve responsive to. couplingactuating huid-pressure aswell astov said last `mentioned source of vpres, sure adapted tobloek. the flow of fluid through said orice, a further .exhaust passage, and a. Ydifferential valve responsive to coupling Yactuatingfluidpressure as Well asto saidlast mentioned source .of pressure adaptedy to block said. latter passage. K

9. A drive engagement control adapted for use in a self-propelled vehicle having anen'gi-ne. -.a manually ,operated throttle linkage for controle line the Speed .of said engine, a driven shaft-end gradually engageable .coupling .means for estabE lishing .drive between said engine and shait. 00mprising a uid pressure operated mechanism tor eiecting .coupling engagement, a source. of fluid pressure communn.:atinsl with said mechanism .having a .volume capacity. ,increasing with engine speed, .an exhaust orifice also communicating with said mechanism for .controlling the effective coupling .actuatingprcssure a further exhaust passage, mechanism responsive .to the operation cfsad` throttle linkage` for establishing a. ,source of pressure `when .the throttle actuating. linkage is depressed, a differential .valve adapted to block said latter passage, said .valve being urged to an openpostion by couplingactuatng pressure and toa closedposition by pressure from said last mentioned source.

10.. control system .as .set forthintclaim 9 .wherein a certain .minimum coupling actuating pressure is. required-.to vproduce an .initial coupling engagement and wherein said valve is preloaded in closedpositicn in a .manner providing a cou-z plingactuating pressure `less-.than that required for. initial vcoupling engagement notwithstanding a released position of. said Ythrottle actuating.link age... i

11. A clutch control adapted ior'usefinza sel-fpropelled-,vehiclehaving .an engine', .a manually operated throttleiinkaee. for controlling .-thespced oisaidengne, .a driven shaft, and-a friction clutch for establishing drive between said engine -and shaft, comprising a `huid pressure operated nicchenism for -sffeotins .clutch engagement, va source orfiuidgpreSsH-re Communicating with-said mech? al1-ism haring-.a volume capacity increasing Ywith eneinespeed.. an exhaustorince also-communi, eating-with said :mechanism: for: controlling Vthe eifective clutch? :actuating .pressurepmechanism acca-39s '91 responsive Vtoy the ope'rationoi 'said throttle linkage for establishing a-source of pressure varying withthrottle opening, a differential valve adapted to block saidorice, saidl valve being urged to an open position by clutch actuating lpressure and to a blocking position byfpressure from said last mentioned source.

12. A clutch pressure control system as set forth in claim Ii' wherein a certain minimum clutch actuating pressure is required to produce an initial clutch engagement and wherein said valve is urged by resilient means to a blocking position in a manner causing a minimum clutch actuating pressure approaching that required for initial clutch engagementto be maintained independentof engine speed or throttle opening.

13. A clutch control adapted for use in an automatic transmission for a self-.propelledvehicle having an engine, a manually operated mechanism for controlling the speed of said engine, a driven shaft and a iiuid pressure actuated friction clutch for establishing drive between said engine and driven shaft, characterized by a source of clutch actuating fluid pressure having a volume capacity increasing with engine speed, an exhaust orifice for effecting a clutch actuating pres- Sure increasing with the engine speed, and an orifice blocking valve operative to prevent orice discharge during initial stages of build up in clutch engaging pressure. l

14. A clutch pressure control system for an automatic transmission as set forth in claim 13, wherein said valve is responsive to clutch actuating fluid pressure in amanner blocking the ilow of iiuid through said orifice when the actuating pressure is below a predetermined minimum.

15. A clutch pressure control system for an automatic .t-ransmissiongas set forth in claim 13, wherein said valve is differentially responsive to clutch actuating fluid pressure and to the position of saidmanually operated mechanism for blocking the new of fluid through'said orice when the actuating pressure -is below a predetermined minimum varyingv withthe position of said manually operated mechanism.I v

16. In a clutch pressure control system for an automatic transmissionV as set' forth in claim 13, a further exhaust passage, a valve responsive to clutch actuating fluid pressure and to the position of saidmanually operated mechanism adapted to block-the ilow of 'iluid through said -latter passage when said manually operated mechanism is actuated and to open said latter passage when said clutch actuating pressure exceeds a predetermined minimum with said manually operated vmechanism in a released position.

17. In a clutch pressure control system for an automatic transmission as set forth in claim 16, :a differential valve responsive to clutch actuating fluid pressure and to the position of said manually operated mechanism `for blocking the vflow of fluid through said orifice when the actuating pressure is below a predetermined minimum determined by the position of said manually operated mechanism, a further exhaust passage, a valve responsive to clutch actuating fluid pressure and to the position of said manually operated mechanism adapted to block the iiow of fluid through said latter passage when the clutch actuating pressure is below a predetermined minimum or when said manually operated mechanism is in an actuated position and to open said latter passage when said clutch actuating pressure exceeds a predetermined minimum with Isaid manually operated mechanism in a-released position.v

18. A clutch control adapted for use in a selfpropelled vehicle having an engine, a manually operated throttle linkage for controlling the speed of said engine, a driven shaft, and a friction clutch for establishing drive between said engine and shaft, comprising a iiuid pressure operated mechanism for effecting clutch engagement, a source of fluid pressure communicating with said mechanism having a volume capacity increasing with engine speed, an exhaust orice also communicating with said mechanism for controlling the effective clutch actuating pressure, a further exhaust passage, a pressure control valve responsive to the operation of said throttle linkage for establishing a source of pressure varying with the extent of throttle opening, a pair of valves each differentially responsive to said clutch actuating iiuid pressure and said last mentioned source of pressure for controlling respectively the opening of said orice and the opening of said further exhaust passage, said valves being adapted to maintain a predetermined minimum clutch actuating'pressure approaching that required for initial clutch engagement independent of engine speed and to render said orice inoperative until progressively higher minimum clutch actuating pressures are established in accordance with progressively increased throttle openings. and to render high idling engine speeds ineiective to produce initial clutch engagement whenl said throttle linkage is in a released position.

19. A drive engagement control adapted for use ina self-propelled vehicle having an engine, a driven shaft and gradually engageable coupling means for establishing drive therebetween, a fluid pressure operated mechanism for eifecting coupling engagement characterized by a source of iiuid pressure communicating with said mechanism having a volume capacity increasing with engine speed, a coupling engagement pressure regulating exhaust orifice means also communicating with said mechanism in a manner whereby coupling engagement pressure may be made to increase in accordance with engine speed, and a pressure responsive valve mechanism operative to block said orifice means during a preliminaryl build-up of coupling engagement pressure to a predetermined point.

2). A drive engagement control adapted fort use vin a self-propelled vehicle having an engine, a'driven shaft and gradually engageable coupling means for establishing drive therebetween; a fluid pressure operated mechanism for effecting coupling engagement characterized by a source of fluid pressure communicating with said mechanism having a volume capacity increasing with engine speed, a coupling engagement pressure regulating exhaust orifice means also communicating with said mechanism in a manner whereby coupling engagement pressure may be made to increase in accordance with engine speed, and a pressure responsive valve mechanism operative to block said orifice means during a preliminary build-up of coupling engagement pressure to a predetermined point varying with throttle opening.

2l. A clutch control adapted for use in a selfpropelled vehicle having a throttle-controlled engine, a driven shaft and a friction clutch for establishing drive therebetween, comprising a fluid pressure operated mechanism for effecting clutch engagement, and an automatic fluid pressure control system for graduating clutch engagement pressure, said control `system fbeingcharacterized by an engine driven pump, an orice through which the pump output can discharge, -thereby to build up fluid pressurein-the pressure operated mechanism and to increase the clutch engaging pressure as the'speed of the engine increases, means for establishing :a1-control pressure varying With engine throttle opening, and means responsive to said last pressure adapted to close said orce duri-ng the establishment .of predetermined minimumclutch engagement .pressures .increasing with throttle opening.

22. A drive engagement control adapted. or use in a transmission for a self-,propelled vehicle having an engine, a driven shaftandgradually engagea-ble coupling means for establishing .drive therebetween, comprisingk a. uid pressure actuated .mechanism foreiectingcoupling Yengagement, and a uid pressure control .system for regulating the coupling engagement pressure,.said system including a pump operatively. connected to `said fluid pressure actuated. mechanism, a pressure regulating orifice .through whichthe outputfrom said pump can discharge, and an orifice .blocking valve toinhibit ow .through .Said orifice .cap-able of being .actuatedinresponse to the .establishment 4of certain drive .ratios` 23. A clutch control adapted for Yuse in a transmission for self-propelled vehicles vhavingan engine, a driven .shaft and a friction clutchfor `es` tablishing drive therebetween, comprising a uid pressure actuated mechanism for effecting clutch engagement, and a uid pressure control. system for regulating the clutch engagement pressure,

said system Vincluding a pump operatively connected .to said uid pressure actuated mechanism, a pressure regulating ori-nce through which the output from said ,pum-pcan discharge, and an orifice blocking valve to block the now. throughY said orince capable of being actuated .inresponse -to the establishmentof certain transmission ratios.

24.. A drive engagement control adapted -for use in a Self-propelled vehicle having an. engine, a manually controlled throttle, a .driven shaft, and gradually engageable couplingmeans 4for `establishing drive therebetween,-.comprising a uid pressure 'actuated mechanism for effecting coupling engagement, means. for establishing an actuating pressure progressively increasing `with throttle opening to establish partial coupling engagement, the. degree .of which increases with throttle opening, .and pressure .meansresponsive to. engine speed to complete coupling. engagement.

. .2`5....`1i'fdriirer engagementnontrol ndaptemforuse in asalta-propelled rehieleiraringanvengine, a manuallynontralled'thrnttle, a'dnwerrshmftfand gradually: rengageahlef- :coupling z vmeans. for .establishingnrive ftherebetweem comprising a :duid pressure aetuatedvmechaaaism :for f eecting coupling engagement, means responsive 'to .engine Speedtoinmease thezcouplingzengag'ing pressure with increasejn:=enginefspeed, fa coupling pressure Ll-i'mitingfvalve, fandmeaznsforsestablishing ya pressurevarying with. throttle opening, said .last pressure being @adapted actuate "r-saicl pressure limiting valve.

.26.. .A drivef engagement :econtroi system :as set forthminclaimslilnfmither '.-pharacterized .by said orifice dosing' ameri: plate type, 'fand by the :provision .infame ndjnstab'le :orifice whereby? the gelaionship memeenteffecti-ve icoupl-'mg pressinfe .midfengine Speedmay -sbe adiustabl'yvanied.

.zrner'selfepmpeliedwehiele:having an engine, aidriven shaft and aiictinnzelutch forle'stablishingxdriveztherehetween, a fluid `:pressure orne-ratedv mecmnsmoretecting clutch engagement; tand' an. automatici. .fluid-*pressure 'control system .for agradiiatingiplmchngagement pressure fcomprising-uanxeng-ineizdr-iven pump, an orice-throiighrwvhich '.tre-pmnp output can discharge, "thereby todauirld inpui :pressure in the pressure operated mechanismand to .increase the clutch engaging Apressureasthespeed of the engine increases, said price'sbeingnf :a vfixed 'thin plat-e1 type'. to minimize the eie'ct .of changes .in viscosity of-rthe-ui'd'nnthe'pressure built up by the -Lflovvof .fiuidl through it.

T.. LIVERMORE.

.References/@iisd @the 'Lilie `fof-*this patent STATES PATENTS 

